The invention generally relates to double seat valves used for separating media. More specifically, the invention relates to a type of a double seat valve, which comprises a valve housing, which has connectors for a first pipeline and a second pipeline, a first closing member and a first closing member seat assigned thereto, wherein the first closing member in its closed position cooperates in a sealing manner with the first closing member seat via at least one sealing element, and comprising a second closing member axially spaced from the first closing member, and a second closing member seat assigned to said second closing member, wherein the second closing member in its closed position cooperates in a sealing manner with the second closing member seat via at least one sealing element, wherein the two closing members can be lifted independently of one another from their respective closing member seat, wherein a leakage space is provided between the two closing members and discharges into a leakage outlet.
Double seat valves of the above-mentioned type are used for example in the food processing industry in product-conveying processing systems.
With double seat valves of this type, there are high requirements on the reliable separation of the media conveyed through the at least two pipelines. The two closing members in their closed position separate the two connectors tightly with respect to one another on the inner side of the housing, and in the common open position of the two closing members the pipelines connected to the two connectors can communicate with one another via the housing interior.
A further fundamental requirement of such double seat valves lies in the fact that the closing members, including their closing member seats and the leakage space located between the closing members, can be thoroughly cleaned.
In order to avoid the need to switch off all processes in a processing system, in which such a double seat valve is used, for the purpose of cleaning the closing members, the closing members seats and the leakage space, which would reduce the productivity of such a processing system, it is desirable if the cleaning process is carried out for example via one of the two pipelines, whereas a product process continues in the other pipeline. For this purpose, the two closing members can be lifted independently of one another from their closing member seat. The term “lift” is to be understood with such double seat valves to mean that one of the two closing members is moved far enough from its closing member seat by a short stroke that there is no longer any sealing contact between the sealing element of this closing member and the associated closing member seat. Here, the other closing member remains in sealed contact with its closing member seat. A cleaning medium, normally a cleaning liquid, can then be fed into the leakage space through the pipeline and the connector to which the lifted closing member is assigned, via the gap between the closing member and the associated closing member seat, such that the cleaning medium thoroughly rinses the closing member seat of the lifted closing member and the sealing element thereof and the leakage space. The cleaning medium supplied through the connector associated with the lifted closing member is normally under a very high pressure during this process, which may sometimes be 10 bar or more.
The cleaning medium runs via the leakage space to the leakage outlet and, from here, into the surrounding environment of the double seat valve.
Document DE 10 2005 057 103 A1 describes the problem that, when feeding the cleaning medium, no additional overpressure may form in the leakage space in accordance with the provisions of more recent standards, said additional overpressure, in the extreme case, possibly causing the other closing member located in the closed position to be moved away from its closing member seat, such that cleaning medium could enter the other pipeline, in which a product process is currently being carried out.
To solve this problem, it is proposed in that document to provide a closing member with an inclined drainage portion, of which the total opening cross section is at least approximately as large as the opening cross section of the larger of the two connectors. The problem of an overpressure build-up in the leakage space as a result of an excessively low discharge of cleaning medium from the leakage space during the cleaning process is thus avoided, wherein the leakage outlet has a passage cross section corresponding to the cross section of the leakage space in order to satisfy this provision.
However, only the problem of avoiding an overpressure in the leakage space is solved thereby. A further provision of more recent standards is that, when the leakage space is impinged after lifting of one of the two closing members, the at least one sealing element or the closing member seat of the other closing member, which is located in its closed position, is not impinged directly by cleaning medium, because cleaning medium could then also enter the other pipeline, because the cleaning medium as already mentioned is under a high pressure. With the previously mentioned known double seat valve, this provision is not satisfied. If, for example, the lower closing member of the known double seat valve is lifted, and if pressurized cleaning medium is fed into the leakage space in the gap between the closing member and the closing member seat thereof, the cleaning medium, due to its substantially axial direction of flow, initially contacts the closing member seat and the sealing element of the upper closing member located in the closed position, whereby cleaning medium could flow past the sealing element of the upper closing member and infiltrate the valve housing region, through which a product medium currently flows.
The above-mentioned problem is overcome in the case of the double seat valve known from document DE 10 2007 038 124 A1, by a flow barrier element, which, when one closing member is lifted and as the leakage space is impinged by cleaning medium, shadows the at least one sealing element and/or the closing member seat of the other closing member, which is located in its closed position, against direct impingement by the cleaning medium entering the leakage space. The flow barrier element thus prevents the cleaning medium, as it enters the leakage space, from directly impinging the seal and/or the closing member seat of the other closing member located in its closed position.
Various embodiments of the flow barrier element are disclosed in the cited document. In all these embodiments cited in said document of the flow barrier element, it is necessary for the leakage outlet adjoining the leakage space to have at least the same cross section as the leakage space in order to satisfy the provision already mentioned above, in accordance with which no pressure may build up in the leakage space. However, this has the disadvantage that the leakage outlet pipe adjoining the leakage space has to have an accordingly large diameter and therefore a wall with a large circumference. This leads to a greater material outlay and therefore to greater initial costs of the known double seat valve.